Copilot commented on code in PR #3865:
URL: https://github.com/apache/avro/pull/3865#discussion_r3568131040
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lang/java/avro/src/test/java/org/apache/avro/generic/TestGenericDatumReader.java:
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@@ -216,6 +222,30 @@ void arrayOfIntsRejectsHugeCount() throws Exception {
assertThrows(EOFException.class, () -> reader.read(null, decoder));
}
+ /**
+ * On a stream source the decoder cannot know how many bytes remain, so the
+ * bytes-available guard is skipped and a large declared array count reaches
the
+ * allocation path directly. The initial backing-array capacity must be
clamped
+ * so a hostile count cannot drive a huge up-front allocation; a truncated
+ * stream therefore fails with {@link EOFException} (once the declared
elements
+ * cannot be read) rather than attempting to preallocate hundreds of
millions of
+ * slots.
+ */
+ @Test
+ void arrayHugeCountOnStreamClampsPreallocation() throws Exception {
+ Schema schema = Schema.createArray(Schema.create(Schema.Type.LONG));
+ GenericDatumReader<Object> reader = new GenericDatumReader<>(schema);
+
+ // A huge (non-zero-byte) block count followed by no element data.
Wrapping in
+ // a BufferedInputStream keeps the source from being a
ByteArrayInputStream, so
+ // it cannot report its remaining byte count (remainingBytes() == -1) and
the
+ // bytes-available guard is disabled -- exercising the preallocation clamp.
+ byte[] data = encodeVarints(200_000_000L);
+ InputStream stream = new BufferedInputStream(new
ByteArrayInputStream(data));
+ BinaryDecoder decoder = DecoderFactory.get().binaryDecoder(stream, null);
+ assertThrows(EOFException.class, () -> reader.read(null, decoder));
+ }
Review Comment:
`arrayHugeCountOnStreamClampsPreallocation` can miss regressions on
large-heap test runs: if a future change reintroduces `new Object[(int) count]`
preallocation, allocating ~200M slots (~1.6GiB) may succeed on a big CI JVM and
the test would still pass with an `EOFException`. Make the test deterministic
by asserting the decoder is on the unknown-remaining-bytes path and by
overriding `GenericDatumReader.newArray` to assert the initial allocation size
is clamped (via `GenericDatumReader.initialCollectionCapacity(...)`).
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